How about simply PDF::Highlight? I'm guessing that most people will know that they want to highlight words in a PDF without knowing how that actually happens. Spelling out "highlight" and leaving off the HFF let's them find the module with the same keywords they might put into a search engine. :)

You might also like to ask this question on the module admins list, modules@perl.org. There are quite a few people there that can give you good advice about module names. :)